The field of the present invention is sealing mechanisms for a rotating shaft having bearings which are pressure lubricated.
In industrial turbomachinery including turbines, turboexpanders, compressors and the like, a high speed rotor is often employed which is supported by a rotatably mounted shaft. The shaft is in turn mounted in bearings. Such bearings often include a pressurized lubricant system delivering a large amount of lubricating fluids to the bearings. At the same time, working fluid may be pressurized near the shaft such that there is a tendency for that fluid to flow along the shaft toward the pressurized bearings and for the pressurized lubricant to flow toward the rotor cavity and mix with the working fluid. However, contamination of the working fluid by the lubricant is often disadvantageous and can in fact be disastrous to the system.
A number of solutions of varying success have been proposed as a means for creating an adequate seal between the working fluid in the rotor cavity and the lubricant in the pressurized bearing. A simple labyrinth seal for such a device arranged on a tapered portion of the shaft is illustrated in U.S. Pat. No. 4,287,758, the disclosure of which is incorporated herein by reference. The labyrinth seal provides a series of ridges closely approaching the shaft and intermediate channels which are found to substantially reduce the amount of flow therethrough. The tapered arrangement of the shaft provides centrifugal forces tending to direct material within the labyrinth seal toward the bearing.
Additional devices for sealing such a shaft have employed drains and open areas between the bearing and the seal. One such device is illustrated in U.S. Pat. No. 3,360,239, the disclosure of which is incorporated herein by reference. In that patent, a chamber is fully exposed to atmosphere with a separate bearing seal also employed.
An additional mechanism for avoiding contamination of the working fluid is to provide pressurized gas to the seal such that the gas pressure maintains a pressure barrier against flow of lubricant toward the rotor end of the shaft. One such system employing compressed gas as a seal gas is illustrated in U.S. Pat. No. 3,420,434, the disclosure of which is incorporated herein by reference.
The foregoing arrangements for sealing a shaft have several possible objections. A seal gas source and the system for delivering same is required. Additionally, the seal leakage of such systems may be excessive. A third difficulty can be that the seal gas leaks into the process stream and dilutes the working fluid. A pressure upset in such a seal depending on pressure differentials may result in oil being swept into the working fluid before an appropriate response can be taken. The seal gas flow may also be restricted or in some way cut off such that the sealing cannot be fully effected.